High voltage arc discharge lamp with low voltage control circuit



Nov..18, 1969 s. c. PEEK 3,479,558

HIGH VOLTAGE ARC DISCHARGE LAMP WITH LOW VOLTAGE CONTROL CIRCUIT FiledJune 23, 1967 2 E1 :31 L 2 f" X j iii?! United States Patent 3,479,558HIGH VOLTAGE ARC DISCHARGE LAMP WITH LOW VOLTAGE CONTROL CIRCUITSandford C. Peek, Ipswich, Mass., assignor to Sylvania Electric ProductsInc., a corporation of Delaware Filed June 23, 1967, Ser. No. 648,346Int. Cl. H05b 41/14 US. Cl. 315-98 4 Claims ABSTRACT OF THE DISCLOSUREAn electronic circuit for applying periodic ionizing pulses anddischarge current to a fluorescent lamp rated for operation from a 240volt alternating current supply and having heated filaments, the circuitincluding a semiconductor valve for applying the pulses and rated foroperation at 120 volts applied. A transformer whose primary is connectedto the 240 volt supply, has secondaries for supplying heating current tothe lamp filaments and also has a primary tap for supplying 120 volts tothe semiconductor.

Conventional fluorescent lamp starting and operating circuits havecomprised a ballast for applying a high starting voltage to the lamp toionize it and start discharge and for inductively limiting currentthrough the ionized lamp. Because of the weight and bulk of the ballastand its high expense, heating and noise, control circuits have beenproposed which start and control the lamp discharge by variouselectronic switching circuits. Some of the advanced electronicallyvalved circuits comprise pulse generating or gating semiconductor valvefor periodically applying a voltage pulse to the lamp thereby ionizingthe lamp sufliciently to support an arc discharge for a limited period,usually a half-cycle or less of the alternating current supply.Typically the electronic valve is connected in series with a pulsestorage capacitor across the alternating current supply. Frequently thefluorescent lamp and the operating circuit are designed for operatingfrom a 240 volt or greater alternating current supply. But it is highlydesirable for reasons of economy and availability to employ asemiconductor rated at, that is, capable of impeding only about 120volts, and incapable of operating on the 240 volt supply.

While it would be possible to provide a special transformer or otherpower consuming circuit to reduce the supply voltage to that for whichthe semiconductor is rated, it is the object of the present invention touse an existing component of the operating circuit to perform both itsusual function and also the function of providing the rated voltage ofthe semiconductor although only a substantially higher voltagealternating current is available.

According to the invention a circuit for an arc discharge lamp havingheated filaments and operating at a predetermined high voltage comprisesfilament and discharge terminals for connection to a supply of said highvoltage alternating current, a power circuit connecting said powerterminals to said discharge terminals including electronic valve meansfor applying periodic voltage pulses to said discharge terminals therebyto support an arc discharge by ionization in the lamp and to drawcurrent from said alternating current supply, said valve means beingadapted to impede only an applied voltage substantially lower than saidpredetermined high voltage, and a transformer including a primaryconnected between said power terminals, a secondary connected to saidfilament terminals for supplying heating current thereto, and an outputconnected to, and for supplying current to, said valve means atsubstantially lower voltage.

For the purpose of illustration typical embodiments 3,479,558 PatentedNov. 18, 1969 of the invention are shown in the accompanying drawing, inwhich:

The figure is a schematic diagram of high voltage fluorescent lampoperating circuit according to the invention.

As shown in the figure two eight foot HO fluorescent lamps L (which maybe considered as one lamp) have filaments which when heated to emissionprovide a source of electrons for ionizing the mercury vapor and gasfill of the lamp. The filaments f are connected to dischargeterminals 1. The lamps L are designed for operation on a 240 voltsupply. Power for the lamps is supplied from 240 volt, 6O cyclealternating current terminals A and C. Power terminal A is connected toa lamp terminal I through an autotransformer primary T1 and secondary T2having a turns ratio of l to 3 and very low reactance compared to aconventional ballast. Power terminal C is connected directly to a lampterminal I. A core transformer comprises a primary T3 and secondaries T4for supplying heating current at about 3.5 volts to the filaments f. Thecore transformer is of negligible reactance compared to a conventionalballast.

A voltage pulse discharging circuit includes a triac V1 (G.E. typeSC45B), a diac D1 (G.E. type 8T2), a primary voltage pulse storagecapacitor C1 (6 microfarad) a secondary storage capacitor C2 (0.33microfarad) and a coupling capacitor C3 (0.07 microfarad). Separableconnectors 1, 2 and 3 indicate that the coupling capacitor C3 may beconnected by the male connection 1 to either of the two femaleconnectors 2 or 3. Connector 2 leads through a resistor R1 kilohms) to ajunction between capacitor C1 and valve V1. Connector 3 leads directlyto the power terminal A. The primary storage capacitor C1 and triac T1are connected in series through the autotransformer primary T1, so thatduring each half-cycle of alternating current the primary storagecapacitor C1 charges through the triac T1. In the succeeding half-cyclethe voltage across the secondary capacitor C2 rises toward the breakdownvoltage of the diac D1. When this breakdown voltage is exceeded the diacD1 conducts allowing the secondary capacitor C2 to discharge to the gateelectrode g of the triac and trigger the triac into avalancheconduction. The primary capacitor then discharges through the triac andautotransformer primary and reverses its charge. The discharge voltageis stepped up by the l to 3 ratio of primary to secondary, and thestepped up voltage (e.g. 600 volts peak) is applied to the lampterminals I. At this instant a limited number of ions are established inthe lamps L, and the lamps fully ignite and conduct line current forpart or all of the half-cycle. About when the line voltage passesthrough zero the arc tends to extinguish, but does not if amplitude andduration of the ionizing pulse has produced suflicient ionization tomaintain discharge until the next succeeding ionizing pulse is applied.

While alternating current is supplied to the lamps L at 240 volts, amore economical and available triac and diac, rated for volt operation,are used. According to the invention no components need be added to theabovedescribed circuit. A tap t, mid-way between the ends of theexisting filament transformer primary T3, is connected to one primaryelectrode ec of the triac. The RMS voltage of 120 volts provided by thetap t is correct for the rated voltage of the triac and diac, and is inphase with the alternating current applied to the lamp. Furthermore, theaddition of bulky and power-consuming low voltage sources is avoided.

Accordingly it should be understood that this disclosure is for thepurpose of illustration only and that the invention includes allmodifications and equivalents falling within the scope of the appendedclaims. For example, other electronic valves, such as two Delco type2N1412 transistors rated for relatively low voltage operation, may beconnected in parallel in opposite polarity to apply ionizing pulses tothe lamps.

I claim:

1. A circuit for operating an arc discharge lamp having heated filamentsand operating at a predetermined high voltage comprising:

filament and discharge terminals for connection to the lamp,

power terminals for connection to a supply of said high voltagealternating current,

a power circuit connecting said power terminals to said dischargeterminals,

a pulse discharging circuit including electronic valve means forapplying periodic voltage pulses to said discharge terminals therebycausing the lamp to support an arc discharge by ionization in the lampand to draw current from said alternating current supply, said valvemeans being adapted to impede only an applied voltage substantiallylower than said predetermined high voltage,

a transformer including a primary connected between said powerterminals, a secondary connected to said filament terminals forsupplying heating current thereto, and an output connected to, and forsupplying current to, said valve means at said substantially lowervoltage, and

additional means compling said valve means to said discharge terminals.

2. A circuit according to claim 1 wherein said transformer outputcomprses a tap connected intermediate the ends of said primary.

3. A circuit according to claim 1 wherein said transformer is connectedto step down the voltage at said power terminals.

4. A circuit according to claim 1 wherein said additional coupling meansincludes a step-up transformer connected between said valve means andsaid discharge terminals.

References Cited UNITED STATES PATENTS 3,l70,085 2/196'5 Genuit 3l5-273X 3,235,769 2/1966 Wattenbach 3l5176 3,336,501 8/1967 Segawa 315-289 XJAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant ExaminerUS. Cl. X.R.

